The present invention relates to a Grignard-type process for the preparation of unsaturated organic compounds. The process comprises contacting an unsaturated organic halide with magnesium metal in a mixture of ether and a polar halogenated hydrocarbon co-solvent, filtering the reaction product from the reaction step and thereafter, treating the reaction product filtrate from the filtration step to obtain the desired unsaturated organic compounds.
The inventors of the present invention have found that the use of halogenated solvents in conjunction with ethers, the traditional Grignard reaction solvents, results in lower reaction temperatures, the ability to separate the desired unsaturated organic compounds from the by-produced magnesium halides with ease which results in higher yields of purer unsaturated organic compounds.
The reaction of organic halides with magnesium metal in the presence of oxygenated solvents such as dialkyl ethers to form reactive complexes typically referred to as Grignard reagents is well known. The production and reactions of Grignard reagents has been the subject of books and numerous review articles. Such reviews are provided, for example, in Coates, et al., ORGANOMETALLIC COMPOUNDS, Vol. 1, pp. 76-103, (1967), Methuen and Co. Ltd, London, U.K.; and in Kirk/Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 10, 721-734 (1966), The Interscience Encyclopedia, Inc., NY, N.Y. The structure of the Grignard reagent has not been determined with certainty, however it is generally believed that the Grignard reagent exists as a complex in solution and that solvent can play a critical role in such complex formation. The unpredictable effect of solvent on the formation and reactivity of Grignard reagents is discussed in the above cited review articles, and the inventors herein believe, but should not be held to such a theory, that the following reaction equations may be the actual mechanisms, using allyl chloride as the organic halide reactant example: 
The preparation of unsaturated organic compounds such as 1,5-hexadiene by a process using a Grignard reagent as an intermediate is known. For example, Turk, et al., Organic Synthesis, Vol. 27, 7-8, 1947, teach a process for preparing 1,5-Hexadiene by the reaction of allyl chloride in anhydrous ether with magnesium turnings. Turk et al. teach that this reaction results in the formation of a thick slurry that becomes unstirrable. This unstirrable slurry is then treated with a hydrochloric acid solution until enough of the chloride by-product is in solution and then the slurry becomes sufficiently fluid to be stirred.
Such processes as taught by Turk et al. are not generally acceptable as a commercial process. The formation of the unstirrable slurry during the reaction can cause reduced mass transfer and heat transfer and therefore reduced yields. Furthermore, the nature of the slurry makes it necessary to treat the slurry in an additional step with a reagent to solubilize the slurry to allow isolation of the product. Typically, a major portion of the product is trapped with the unstirrable slurry. In addition, the non-flowable nature of the slurry does not allow for the reaction to be run as a large scale or continuous process.
A further disclosure regarding the use of the Grignard technology to prepare unsaturated organic compounds can be found in U.S. Pat. No. 5,596,120, that issued to Bank, et al., on Jan. 21, 1997 in which an attempt is made to overcome the drawbacks of the Turk, et al. process. Therein, Bank et al. teach that organosilanes can be prepared using magnesium metal with a mixture comprising an organic halide and a halosilane in a co-solvent comprising about one to 15 mole of a dialkyl ether comprising less than seven carbon atoms, per mole of allyl chloride, and about 0.05 to less than two mole of a liquid aromatic hydrocarbon solvent per mole of the dialkyl ether, at a temperature within a range of about 5xc2x0 C. to 200xc2x0 C. The taught hydrocarbon solvent is toluene. No mention is made in this disclosure about the use of chlorinated hydrocarbon solvents and the benefits achieved by their use in the Grignard technology.
Another disclosure is that found in European Patent Specification EP 0 729 931 to Hayes II, et al., in which there is disclosed a one-step Grignard-type process for the preparation of 1,5-Hexadiene. The process comprises contacting magnesium metal with a mixture comprising allyl chloride; one to 15 mole of a dialkyl ether comprising less than seven carbon atoms, per mole of the allyl chloride; and 0.05 to less than two mole of a liquid aromatic hydrocarbon solvent per mole of the dialkyl ether at a temperature within a range of 5xc2x0 C. to 200xc2x0 C. The liquid aromatic hydrocarbon solvent is disclosed as toluene and there is no mention in this disclosure with regard to the use of chlorinated hydrocarbon solvents for use in preparing unsaturated organic compounds. It is alleged that this process provides easily stirred slurries which improve mass transfer and heat transfer during the process and allows for easier separation of the unsaturated organic compound from the product slurry. Furthermore, it is noted therein, that the method allows for the process to be run as a continuous process.
The present invention thus deals with a process of preparing unsaturated organic compounds using a Grignard-type reaction technology wherein magnesium metal is contacted with an unsaturated organic halide in the presence of an ether and a polar halogenated hydrocarbon co-solvent or a mixture of ether and a mixture of polar halogenated hydrocarbon co-solvents.
Thus, what is disclosed and claimed herein is a method for the preparation of unsaturated organic compounds wherein the method comprises contacting an unsaturated organic halide with magnesium metal in a mixture of ether and a polar halogenated hydrocarbon co-solvent or a mixture of ether and a mixture of polar halogenated hydrocarbon co-solvents to produce the unsaturated organic compound. Thereafter, filtering the reaction product and treating the reaction product filtrate to obtain the desired unsaturated organic compounds.
A further embodiment of this invention is a method for the preparation of unsaturated organic compounds wherein the method comprises contacting an unsaturated organic halide with magnesium metal in a mixture of ether and a polar halogenated hydrocarbon co-solvent or a mixture of ether and a mixture of polar halogenated hydrocarbon co-solvents wherein the temperature is in the range of from 5xc2x0 C. to 200xc2x0 C. and most preferred range is from 50xc2x0 C. 100xc2x0 C., and the pressure is in the range of from ambient pressure to about 200 psig wherein the most preferred range is from 0 psig to about 125 psig.
Both of these embodiments are known as xe2x80x9cone-stepxe2x80x9d processes for the preparation of unsaturated organic compounds because it is not necessary to isolate an intermediate Grignard-type reagent in the process and then further react this Grignard-type reagent with the unsaturated organic halide to form the unsaturated organic compounds. Further, it is not necessary to conduct a separate solubilization step on the resulting product slurry to facilitate recovery of the unsaturated organic compound.
The magnesium metal used in this invention can be any of the known forms of the metal that are currently used for Grignard-type reactions. For example, the metal can be any of those known in the art that are in the form of powder, flakes, granules, chips, lumps, and shavings, and the like.
Contact of the magnesium metal with the unsaturated organic halide can be undertaken in standard type reactors suitable for running Grignard type reactions. The reactor can be a batch, semi-batch, or continuous type of reactor. A preferred reactor is a continuous reactor. The environment in which the present method is carried out should be inert for best results. Therefore, in a preferred method, the reactor is purged and blanketed with an inert gas such as, for example, nitrogen or argon.
Generally, the magnesium metal is placed in the reactor containing a co-solvent mixture. The unsaturated organic halide in additional co-solvent is then fed to the reactor at a controlled rate. The mole ratio of magnesium to the unsaturated organic halide fed to the reactor is not critical and can be varied within wide limits. In a batch process, it is preferred that the final mole ratios of magnesium to unsaturated organic halide provide the unsaturated organic halide in sufficient excess to ensure essentially total conversion of the magnesium to the magnesium salts. When the present process is conducted as a continuous process, the magnesium metal is typically present in excess in relation to the unsaturated organic halide fed to the reactor. In such a case, the rate of feed of the unsaturated organic halide to the reactor can be controlled to ensure acceptable levels of conversion of the unsaturated organic halide to the unsaturated organic compounds and, minimal presence of the unreacted unsaturated magnesium halide complexes. Any excess unsaturated organic halide can be captured and recycled to the reactor.
Unsaturated organic halides useful in this invention are described by the formula RX, wherein R is an unsaturated hydrocarbon group comprising about one to 12 carbon atoms and X is selected from a group consisting of chlorine and bromine atoms. The preferred substituent X for the unsaturated organic halide is the chlorine atom. The substituent R can be a substituted or unsubstituted unsaturated hydrocarbon group comprising one to 12 carbon atoms. The substituent R can be, for example, alkenyl or cycloalkenyl. Specific examples of R substituents include vinyl, allyl, hexenyl, pentenyl, cyclopentyl, and cyclopentenyl. Preferred for this invention is the substituent allyl wherein the most preferred unsaturated organic halide is allyl chloride.
The dialkyl ethers useful in this invention include, for example, dimethyl ether, diethyl ether, ethylmethyl ether, n-butylmethyl ether, n-butylethyl ether, di-n-butyl ether, di-isobutyl ether, isobutylmethyl ether, and isobutylethyl ether, and the like. The preferred ether is diethyl ether. It is preferred that the amount of ether in the co-solvent mixture be as small as is possible and therefore, it is preferred that the ratio of ether to the polar halogenated hydrocarbon co-solvent be in the range of about 0.2:2 to 0.5:2.
The polar halogenated hydrocarbon solvent can be any polar halogenated hydrocarbon solvent that is a liquid under process conditions. The polar halogenated hydrocarbon solvent can be, for example, halogenated aromatic solvents, or a combination of them, or aliphatic halogenated solvents, or a combination of them, or a combination of aromatic and aliphatic halogenated hydrocarbons. Preferred for this invention are the aromatic halogenated solvents, and most preferred is chlorobenzene. It should be noted that when any aliphatic halogenated solvent is used, it should be an aliphatic halogenated solvent that reacts with magnesium slower than the formed Grignard reagent since the aliphatic halogenated compounds are more reactive than the aromatic halogenated compounds.
The mole ratio of the dialkyl ether to the polar halogenated solvents is critical to the present process. The present method requires that the amount of ether that is present be as low as possible, meaning that a high ratio of the halogenated solvent to the ether is desired. This is because it is believed by the inventors herein that the halogenated hydrocarbon solvent aids in the precipitation of the very fine MgCl2 that is formed during the reaction and substantially aids in the removal of such salts. Thus, for purposes of this method, the ratio of the total ether to the halogenated solvents should be in the range of about 0.5:2to 1:1.
The inventors herein have discovered that this method provides very low viscosity slurries from which the MgCl2 can be separated easily and essentially completely that leads to substantial improvements in mass transfer and allows for a significant reduction in the total amount of solvent required for the reaction when compared to prior art methods. In addition, this method does not lead to isomerization or polymerization of the unsaturated materials. Generally, this method does not require an initiator for the reaction.